Recently a shelf-stable, fast curing, one component, alkoxy-functional, room temperature vulcanizable (RTV) composition was disclosed in the patent of White et al., U.S. Pat. No. 4,395,526, and assigned to the same assignee as the present invention. Basically, White et al. disclose that moisture curable polyalkoxy-terminated organopolysiloxane RTV compositions can be prepared by combining (1) a silanol-terminated polydiorganosiloxane base polymer; (2) a crosslinking silane; (3) an effective amount of certain silane scavengers for chemically combined hydroxy radicals; and (4) an effective amount of a condensation catalyst. The scavenger, which can be either a separate compound or part of the alkoxy-functional crosslinking agent, has a functionality selected from the group consisting of oximato, carbamato, enoxy, amido, amino, imidato, ureido, isocyanato and thioisocyanato. The disclosure of White et al. is incorporated herein by reference.
Other scavenger compositions that can be utilized in the White et al. composition are disclosed in copending patent applications by R. T. Swiger and J. E. Hallgren, Ser. No. 476,000, filed Mar. 17, 1983; G. M. Lucas, Ser. No. 464,443, filed Feb. 7, 1983 now U.S. Pat. No. 4,503,209; R. H. Chung, Ser. No. 338,518, filed Jan. 11, 1982 now U.S. Pat. No. 4,424,157; and T. D. Mitchell, Ser. No. 462,949, filed Feb. 1, 1983 now U.S. Pat. No. 4,483,972. However, of particular interest are the silazane and silicon-nitrogen polymer scavengers disclosed in copending patent applications by J. J. Dziark, Ser. No. 349,695, filed Feb. 17, 1982 and now U.S. Pat. No. 4,417,042, and R. H. Chung et al., Ser. No. 428,038, filed Sept. 28, 1982. The disclosures of the Dziark and Chung et al. applications are also incorporated by reference into the instant application.
Dziark discloses that the silane scavenger for hydroxy functional groups of White et al. can be replaced with a scavenger selected from silicon-nitrogen compounds selected from the group consisting of:
(A) silicon-nitrogen compounds of the formula ##STR1## where Y is selected from R"' and R"N-- and (B) silicon-nitrogen polymers comprising (1) from 3 to 100 mole percent chemically combined structural units selected from the group consisting of units having the formula: ##STR2## and (2) from 0 to 97 mole percent chemically combined structural units of the formula ##STR3## and mixtures thereof where the silicon atoms of said silicon-nitrogen polymer are joined to each other by a member selected from an SiOSi linkage and an Si N R" Si linkage, the free valences of said silicon atoms, other than those joined to oxygen to form a siloxy unit and nitrogen to form a silazy unit, are joined to a member selected from an R"' radical and an (R").sub.2 N radical, and where the ratio of the sum of said R"' radicals and said (R').sub.2 N radicals to the silicon atoms of said silicon-nitrogen polymer has a value of 1.5 to 3, inclusive, R" is selected from the group consisting of hydrogen, C.sub.1-12 monovalent hydrocarbon radicals and C.sub.1-12 fluoroalkyl radicals, R"' is selected from the group consisting of hydrogen, monovalent hydrocarbon radicals and fluoroalkyl radicals, and c is a whole number from 0 to 3 inclusive. According to Dziark, a preferred scavenger compound is hexamethyldisilazane. PA1 (A) a polydiorganosiloxane base polymer wherein the silicon atom at each chain end is terminated with at least two alkoxy radicals; PA1 (B) an effective amount of condensation catalyst; PA1 (C) a stabilizing amount of a silicon-nitrogen compound for scavenging hydroxy radicals which releases ammonia as a by-product of the scavenging reaction; and PA1 (D) an effective amount of a scavenger for said ammonia by-product selected from the group consisting of molecular sieves, acids, and mixtures thereof. PA1 (A) a polydiorganosiloxane base polymer wherein the silicon atom at each chain end is terminated with at least two alkoxy radicals; PA1 (B) an effective amount of condensation catalyst; PA1 (C) a stabilizing amount of a silicon-nitrogen compound for scavenging hydroxy radicals which releases ammonia as a by-product of the scavenging reaction; and PA1 (D) an effective amount of a scavenger for said ammonia by-product selected from the group consisting of molecular sieves and acids. PA1 (A) a silanol-terminated polydiorganosiloxane base polymer; PA1 (B) an effective amount of condensation catalyst; PA1 (C) a stabilizing amount of a silicon-nitrogen compound for scavenging hydroxy radicals which releases ammonia as a by-product of the scavenging reaction; PA1 (D) an effective amount of a crosslinking silane of the formula ##STR9## where R.sup.1 is a C.sub.1-18 aliphatic organic radical selected from the group consisting of alkyl, alkylether, alkylester, alkylketone and alkylcyano or a C.sub.7-13 monovalent substituted or unsubstituted hydrocarbon radical; and e equals 0 or 1; PA1 (E) an effective amount of a co-catalyst or curing accelerator selected from the group consisting of substituted guanidines, amines, and mixtures thereof; and PA1 (F) an effective amount of a scavenger for said ammonia by-product of the hydroxy scavenger selected from the group consisting of molecular sieves, acids and mixtures thereof. PA1 (A) a silicon-nitrogen compound having the formula ##STR10## where Y is selected from R"' and R".sub.2 N-- and (B) a silicon-nitrogen polymer comprising (1) from 3 to 100 mole percent chemically combines structural units selected from the group consisting of units having the formula ##STR11## and (2) from 0 to 97 mole percent chemically combined structural units represented by the formula ##STR12## where the silicon atoms of said silicon-nitrogen polymer are joined to each other by a member selected from an SiOSi linkage and an SiNR"Si linkage, the free valences of said silicon atoms other than those joined to oxygen to form a siloxy unit and nitrogen to form a silazy unit are joined to a member selected from an R"' radical and an R".sub.2 N radical, and where the ratio of the sum of said R"' radicals and said R".sub.2 N radicals to the silicon atoms of said silicon-nitrogen polymer has a value of 1.5 to 3 inclusive, and R" is a member selected from the group consisting of hydrogen, monovalent hydrocarbon radicals and fluoroalkyl radicals, R.sup."' is a member selected from the group consisting of hydrogen, monovalent hydrocarbon radicals and fluoroalkyl radicals, and c is a whole number equal to 0 to 3 inclusive.
Chung et al. provided an improvement over Dziark in that silazane compounds and silicon-nitrogen polymers were provided which could be utilized as integrated scavengers and crosslinkers. The scavengers disclosed by Chung et al. are selected from the group consisting of non-cyclic silyl nitrogen compounds of the formula ##STR4## and cyclic silyl nitrogen compounds having at least one unit of the formula ##STR5## any remaining units having the formula ##STR6## where R.sup.10 is a C.sub.1-18 aliphatic organic radical selected from the group consisting of alkyl, alkylether, alkylester, alkylketone, alkylcyano and aryl; R.sup.11 is a C.sub.1-18 monovalent substituted or unsubstituted hydrocarbon radical, Q is a radical selected from the group consisting of hydrogen C.sub.1-18 monovalent substituted or unsubstituted hydrocarbon radicals and radicals of the formula ##STR7## where R.sup.10 and R.sup.11 are as previously defined; a varies from 0 to 2, f varies from 0 to 3, h is 0 or 1, s is a whole number from 1 to 10, d is a whole number from 1 to 5, A is selected from the group consisting of hydrogen, C.sub.1-18 monovalent substituted or unsubstituted hydrocarbon radicals and radicals of the formula ##STR8## where R.sup.10 and R.sup.11 are as previously defined; g varies from 0 to 3, R.sup.12 is the same as R.sup.10, R.sup.13 is the same ar R.sup.11 and R.sup.14 is the same as R.sup.11. In each instance the scavenger of Chung et al. must have at least one hydrocarbonoxy group so that the scavenger functions as an integrated scavenger-crosslinker.
One disadvantage of the hydroxy scavengers of Dziark and Chung et al. is that ammonia is produced as a by-product of the scavenging reaction. As a result, the head space of bulk containers, such as 55 gallon drums, may contain substantial amounts of ammonia. This accumulation of ammonia can be so great as to cause severe eye and throat irritation when the drum is opened.
Accordingly, it is an object of the present invention to provide one-component, alkoxy functional silicone RTV compositions in which ammonia by-product is substantially avoided by reaction with an ammonia scavenging compound.
It is another object of the present invention to provide a method for producing silicone RTV compositions which include scavengers for ammonia by-product.
These and other objects and advantages of the present invention will be obvious from the following detailed description.